Field of the Invention
The present invention relates to a door impact beam for a vehicle.
A door impact beam being a reinforcement member is attached inside a vehicle door such as an automobile and the like to suppress the deformation of a vehicle interior caused when a vehicle has a collision or rolls sideways and the like.
Background Art
In recent years, the beam main body of the door impact beam is formed of an iron-based material because it requires stiffness, and a door outer panel, on the other hand, is formed of aluminum alloy to make the panel lightweight.
A painting process is performed with the door impact beam attached to the vehicle door. Exposing them to high temperature when dried in the painting process may cause a distortion on a panel surface due to the plastic deformation of the outer panel of the vehicle door because a heat expansion coefficient is different between aluminum alloy and iron to cause a difference in thermal expansion between the door outer panel formed of aluminum alloy and the beam main body formed of iron.
Up to now, in order to suppress the above distortion, the difference in thermal expansion between the aluminum alloy and iron has been absorbed such that a bolt for attaching an attachment bracket provided on both ends of the beam main body to the vehicle door is kept loose without the bolt being completely tightened at the step before the painting process, and then the bolt is tightened to fix the door impact beam to the door outer panel after the painting process is finished (refer to JP-A-2003-252057 corresponding to U.S. Pub No. U.S. 2003/0160476A1).
Attaching the attachment bracket formed of an iron-based material to the vehicle door formed of aluminum alloy may cause electrolytic corrosion and the like therebetween. In order to prevent the electrolytic corrosion, the attachment bracket may be formed of two components of a first bracket composed of an iron-based material securely installed to the beam main body and a second bracket composed of aluminum alloy which can be attached to the vehicle door, in addition, the difference in the thermal expansion may be absorbed such that the first and second brackets are fastened to by a fastening bolt, the fastening bolt is kept loose without the bolt being completely tightened at the step before the painting process, and then the bolt is tightened after the painting process is finished.
A technique has been known in which a first bracket is provided at both ends of the beam main body, a second bracket is provided at the vehicle door, a long hole parallel to the axial direction of the first bracket is bored therein, and a round hole is bored in the second bracket to fix the long hole to the round hole by a fastening bolt (Refer to JP-U-H05-24118). The technique may be applied to the technique discussed in the above JP-A-2003-252057.
In the related art discussed in JP-U-H05-24118, however, the door impact beam needs to be attached to the vehicle door with the fastening bolt for fastening the first and second brackets kept loose. In this case, the second bracket is swung against the first bracket to cause a problem that makes it difficult to align the second bracket with the outer panel of the vehicle door.
When the door impact beam is attached to the vehicle door, the first and second brackets are fastened by the fastening bolt to fix the mutual positional relationship and the fastening bolt may be loosened after the attachment to absorb the above-mentioned difference in thermal expansion, however, which increases and complicates working processes.
The present invention has been made to propose a door impact beam for a vehicle in which the above problems have been solved.